Atomic Add (ATMCADD)

Built-in number for ATMCADD4 is 671.
ATMCADD4 (
          op1   : address of a signed binary(4) value  (has
                   alignment restrictions
                   - see description below)
          op2   : signed binary(4) value
) : signed binary(4)
 
Built-in number for ATMCADD8 is 672.
ATMCADD8 (
          op1   : address of a signed binary(8) value  (has
                   alignment restrictions
                   - see description below)
          op2   : signed binary(8) value
) : signed binary(8)

Description:   Atomically increments the value pointed to by op1 by the value op2. Returns the original value pointed to by op1.

The value pointed to by op1 and the op2 value must have the same length. Failure to have the operands the same length will not be detected and the results of the instruction are undefined when this occurs.

The first operand must be aligned based on its length:

• four byte length - 4-byte aligned

• eight byte length - 8-byte aligned

The arithmetic performed by this instruction will not signal any exceptions.

This operation is useful when a variable is shared between two or more threads. When updating such a variable, it is important to make sure that the entire operation is performed atomically (not interruptible). See Atomicity for additional information.

The primary purpose of this instruction is to manipulate a variable which is shared by two or more threads, but this instruction does not synchronize storage. When sharing more than one variable between multiple threads or processes, be aware of storage synchronization issues. See Storage Synchronization Concepts for additional information.

Authorization Required

• None

Lock Enforcement

• None

Exceptions

06 Addressing

• 0601 Space Addressing Violation
• 0602 Boundary Alignment
• 0603 Range

08 Argument/Parameter

• 0801 Parameter Reference Violation

10 Damage Encountered

• 1004 System Object Damage State
• 1044 Partial System Object Damage

1C Machine-Dependent

• 1C03 Machine Storage Limit Exceeded

20 Machine Support

• 2002 Machine Check
• 2003 Function Check

22 Object Access

• 2201 Object Not Found
• 2202 Object Destroyed
• 2203 Object Suspended
• 2208 Object Compressed
• 220B Object Not Available

24 Pointer Specification

• 2401 Pointer Does Not Exist
• 2402 Pointer Type Invalid

2C Program Execution

• 2C04 Branch Target Invalid

36 Space Management

• 3601 Space Extension/Truncation

44 Protection Violation

• 4401 Object Domain or Hardware Storage Protection Violation
• 4402 Literal Values Cannot Be Changed